Optimizing core utilization in neurosynaptic systems

ABSTRACT

In one embodiment, a computer program product for optimizing core utilization in a neurosynaptic network includes a computer readable storage medium having program instructions embodied therewith, where the computer readable storage medium is not a transitory signal per se, and where the program instructions are executable by a processor to cause the processor to perform a method including identifying, by the processor, one or more unused portions of a neurosynaptic network, and for each of the one or more unused portions of the neurosynaptic network, disconnecting, by the processor, the unused portion from the neurosynaptic network.

This invention was made with Government support under HR0011-09-C-0002awarded by Defense Advanced Research Projects Agency (DARPA). TheGovernment has certain rights in this invention.

BACKGROUND

The present invention relates to neurosynaptic systems, and morespecifically, this invention relates to optimizing the usage ofneurosynaptic cores of a neurosynaptic system.

Core-based neurosynaptic systems are built of multiple neurosynapticcores, where the neurosynaptic cores are configured and connected toform a network. A single neurosynaptic chip contains a fixed number ofneurosynaptic cores. Chips of various sizes, i.e., number of cores, canbe manufactured. To implement a neurosynaptic system, one or more chipsare needed. In general, it is desired to minimize the number of chipsused by the system. This goal can be served by minimizing the number ofcores.

BRIEF SUMMARY

In one embodiment, a computer program product for optimizing coreutilization in a neurosynaptic network includes a computer readablestorage medium having program instructions embodied therewith, where thecomputer readable storage medium is not a transitory signal per se, andwhere the program instructions are executable by a processor to causethe processor to perform a method including identifying, by theprocessor, one or more unused portions of a neurosynaptic network, andfor each of the one or more unused portions of the neurosynapticnetwork, disconnecting, by the processor, the unused portion from theneurosynaptic network.

In another embodiment, a system includes a processor, and logicintegrated with the processor, executable by the processor, orintegrated with and executable by the processor, where the logic isconfigured to identify one or more unused portions of a neurosynapticnetwork, and for each of the one or more unused portions of theneurosynaptic network, disconnect the unused portion from theneurosynaptic network.

In another embodiment, a computer program product for optimizing coreutilization in a neurosynaptic network includes a computer readablestorage medium having program instructions embodied therewith, where thecomputer readable storage medium is not a transitory signal per se, andwhere the program instructions are executable by a processor to causethe processor to perform a method including identifying, by theprocessor, independent blocks of a first plurality of cores of aneurosynaptic network, and reconfiguring, by the processor, theindependent blocks onto the first plurality of cores by calculating anew mapping for at least one of the independent blocks, and moving, bythe processor, the at least one of the independent blocks to a newlocation on a different core of the first plurality of cores of theneurosynaptic network in accordance with the new mapping.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a network architecture, in accordance with oneembodiment.

FIG. 2 shows a representative hardware environment that may beassociated with the servers and/or clients of FIG. 1, in accordance withone embodiment.

FIG. 3A illustrates a neurosynaptic core circuit, in accordance with anembodiment of the invention.

FIG. 3B illustrates a neurosynaptic network, in accordance with anembodiment of the invention.

FIG. 4A illustrates a method for optimizing core utilization inneurosynaptic systems, according to one embodiment.

FIG. 4B illustrates a method for identifying and removing one or moreunused portions of a neurosynaptic network, in accordance with anembodiment.

FIG. 5A illustrates a method for optimizing core utilization inneurosynaptic systems, according to one embodiment.

FIG. 5B illustrates a neurosynaptic core containing a plurality ofindependent blocks, according to one embodiment.

FIG. 6A illustrates a neurosynaptic core of a non-optimizedneurosynaptic network, in accordance with one embodiment.

FIG. 6B illustrates another neurosynaptic core of the non-optimizedneurosynaptic network, in accordance with one embodiment.

FIG. 6C illustrates a reconfigured neurosynaptic core, according to anembodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

The following description discloses several preferred embodiments ofsystems, methods and computer program products for optimizing coreutilization in neurosynaptic systems.

In the various embodiments described below, one or more neurosynapticcores of a neurosynaptic network may be analyzed, and then modified toreduce the number of utilized cores while preserving the computationalfunctionality of the original neurosynaptic network. The resultingneurosynaptic network may perform the same computation as the originalneurosynaptic network while reducing a footprint of the network and/orconsuming less power. Such a benefit may be realized by identifying andremoving unused portions of the neurosynaptic network, splitting one ormore cores into independent blocks, and moving at least a portion of theindependent blocks to other cores without affecting the overall networkfunctionality.

In one general embodiment, a computer-implemented method is provided foroptimizing core utilization in a neurosynaptic network. Thecomputer-implemented method comprises identifying one or more unusedportions of a neurosynaptic network. Additionally, thecomputer-implemented method comprises, for each of the one or moreunused portions of the neurosynaptic network, disconnecting the unusedportion from the neurosynaptic network.

In another general embodiment a computer-implemented method is providedfor optimizing core utilization in a neurosynaptic network. Thecomputer-implemented method comprises identifying independent blocks ofa first plurality of cores of a neurosynaptic network. Moreover, thecomputer-implemented method comprises reconfiguring the independentblocks onto the first plurality of cores by calculating a new mappingfor at least one of the independent blocks, and moving the at least oneof the independent blocks to a new location on a different core of thefirst plurality of cores of the neurosynaptic network in accordance withthe new mapping.

In another general embodiment, a computer program product is providedfor optimizing core utilization in a neurosynaptic network. The computerprogram product comprises a computer readable storage medium havingprogram instructions embodied therewith. The program instructions areexecutable by a processor to cause the processor to identify one or moreunused portions of a plurality of cores of a neurosynaptic network.Also, the program instructions are executable by the processor to causethe processor to, for each of the one or more unused portions of theplurality of cores of the neurosynaptic network, disconnect the unusedportion from the neurosynaptic network. Moreover, the programinstructions are executable by the processor to cause the processor toidentify independent blocks of the plurality of cores of theneurosynaptic network. Still yet, the program instructions areexecutable by the processor to cause the processor to reconfigure theindependent blocks onto the plurality of cores by calculating a newmapping for at least one of the independent blocks, and moving the atleast one of the independent blocks to a new location on a differentcore of the neurosynaptic network in accordance with the new mapping.

FIG. 1 illustrates an architecture 100, in accordance with oneembodiment. As shown in FIG. 1, a plurality of remote networks 102 areprovided including a first remote network 104 and a second remotenetwork 106. A gateway 101 may be coupled between the remote networks102 and a proximate network 108. In the context of the presentarchitecture 100, the networks 104, 106 may each take any formincluding, but not limited to a LAN, a WAN such as the Internet, publicswitched telephone network (PSTN), internal telephone network, etc.

In use, the gateway 101 serves as an entrance point from the remotenetworks 102 to the proximate network 108. As such, the gateway 101 mayfunction as a router, which is capable of directing a given packet ofdata that arrives at the gateway 101, and a switch, which furnishes theactual path in and out of the gateway 101 for a given packet.

Further included is at least one data server 114 coupled to theproximate network 108, and which is accessible from the remote networks102 via the gateway 101. It should be noted that the data server(s) 114may include any type of computing device/groupware. Coupled to each dataserver 114 is a plurality of user devices 116. User devices 116 may alsobe connected directly through one of the networks 104, 106, 108. Suchuser devices 116 may include a desktop computer, lap-top computer,hand-held computer, printer or any other type of logic. It should benoted that a user device 111 may also be directly coupled to any of thenetworks, in one embodiment.

A peripheral 120 or series of peripherals 120, e.g., facsimile machines,printers, networked and/or local storage units or systems, etc., may becoupled to one or more of the networks 104, 106, 108. It should be notedthat databases and/or additional components may be utilized with, orintegrated into, any type of network element coupled to the networks104, 106, 108. In the context of the present description, a networkelement may refer to any component of a network.

According to some approaches, methods and systems described herein maybe implemented with and/or on virtual systems and/or systems whichemulate one or more other systems, such as a UNIX system which emulatesan IBM z/OS environment, a UNIX system which virtually hosts a MICROSOFTWINDOWS environment, a MICROSOFT WINDOWS system which emulates an IBMz/OS environment, etc. This virtualization and/or emulation may beenhanced through the use of VMWARE software, in some embodiments.

In more approaches, one or more networks 104, 106, 108, may represent acluster of systems commonly referred to as a “cloud.” In cloudcomputing, shared resources, such as processing power, peripherals,software, data, servers, etc., are provided to any system in the cloudin an on-demand relationship, thereby allowing access and distributionof services across many computing systems. Cloud computing typicallyinvolves an Internet connection between the systems operating in thecloud, but other techniques of connecting the systems may also be used.

FIG. 2 shows a representative hardware environment associated with auser device 116 and/or server 114 of FIG. 1, in accordance with oneembodiment. Such figure illustrates a typical hardware configuration ofa workstation having a central processing unit 210, such as amicroprocessor, and a number of other units interconnected via a systembus 212.

The workstation shown in FIG. 2 includes a Random Access Memory (RAM)214, Read Only Memory (ROM) 216, an I/O adapter 218 for connectingperipheral devices such as disk storage units 220 to the bus 212, a userinterface adapter 222 for connecting a keyboard 224, a mouse 226, aspeaker 228, a microphone 232, and/or other user interface devices suchas a touch screen and a digital camera (not shown) to the bus 212,communication adapter 234 for connecting the workstation to acommunication network 235 (e.g., a data processing network) and adisplay adapter 236 for connecting the bus 212 to a display device 238.

The workstation may have resident thereon an operating system such asthe Microsoft Windows® Operating System (OS), a MAC OS, a UNIX OS, etc.It will be appreciated that a preferred embodiment may also beimplemented on platforms and operating systems other than thosementioned. A preferred embodiment may be written using XML, C, and/orC++ language, or other programming languages, along with an objectoriented programming methodology. Object oriented programming (OOP),which has become increasingly used to develop complex applications, maybe used.

Now referring to FIG. 3A, a neurosynaptic core circuit 310, also hereinreferred to as a neurosynaptic core 310, is shown in accordance with anembodiment of the invention. The neurosynaptic core 310 is a neural corecircuit. The neurosynaptic core 310 comprises multiple incoming axons315 and multiple neurons 311. Each neuron 311 and each axon 315 hasconfigurable operational parameters. The neurosynaptic core 310 furthercomprises a synaptic crossbar 312 including multiple synapses 331,multiple rows/axon paths 326, and multiple columns/dendrite paths 334.

Each synapse 331 communicates firing events (e.g., spike events orspikes) between an axon 315 and a neuron 311. Specifically, each synapse331 is located at cross-point junction between an axon path 326 and adendrite path 334, such that a connection between the axon path 326 andthe dendrite path 334 is made through said synapse 331. Each axon 315 isconnected to an axon path 326, such that said axon 315 sends spikes tothe connected axon path 326. Each neuron 311 is connected to a dendritepath 334, such that said neuron 311 receives spikes from the connecteddendrite path 334. Each axon 315 may send information in the form of aspike, and the information may then be communicated to connected neurons311, which may perform some computation on the information. In someinstances, the computations performed by the neurons 311 may result innew spikes that are communicated to additional axons 315 on the sameand/or different neurosynaptic core 310.

Each synapse 331 has a synaptic weight. The synaptic weights of thesynapses 331 of the neurosynaptic core 310 may be represented by aweight matrix W, wherein an entry W_(ij) of the matrix W represents asynaptic weight of a synapse 331 located at a row/axon path i and acolumn/dendrite path j of the crossbar 312. In one embodiment, thesynapses 331 are binary memory devices. Each synapse 331 can have aweight “0” indicating that said synapse 331 is non-conducting, or aweight “1” indicating that said synapse 331 is conducting. A learningrule such as spike-timing-dependent plasticity (STDP) may be applied toupdate the synaptic weights of the synapses 331.

For the sake of simplicity, the neurosynaptic core 310 is shown toinclude four axons 315 and five neurons 311, and a corresponding numberof axon paths 326, dendrite paths 334, and synapses 331. It isunderstood that the neurosynaptic core 310 of FIG. 3A is shown forillustrative purposes, and, in various embodiments, the neurosynapticcore 310 may comprise any number of axons and neurons, and correspondingaxon paths, dendrite paths, and synapses. For example, the neurosynapticcore 310 may comprise 64 axons and 64 neurons, 128 axons and 128neurons, 256 axons and 256 neurons, 512 axons and 512 neurons, etc.

FIG. 3B illustrates a neurosynaptic network 350, in accordance with anembodiment of the invention. The neurosynaptic network 350 is a scalableneuromorphic and synaptronic architecture. As shown, the neurosynapticnetwork 350 may include multiple chip structures 370, and each chipstructure 370 comprises multiple neurosynaptic cores 310. Of course, inother embodiments, a neurosynaptic network may comprise only a singlechip structure 370, with the single chip structure 370 includingmultiple neurosynaptic cores 310. Each single chip structure 370 mayinclude any number of neurosynaptic cores 310. For example, a singlechip structure 370 may include 256, 1024, 4096, etc. neurosynaptic cores310.

An event-routing system 375 of the neurosynaptic network 350 routesfiring events between neurosynaptic cores 310 of the chip structures370. A neurosynaptic core 310 of the neurosynaptic network 350 may sendfiring events to, and receive firing events from, another neurosynapticcore 310 of the same chip structure 370 or a different chip structure370.

In one embodiment, the routing system 375 comprises point-to-pointconnections. In another embodiment, the routing system 375 comprisesnetwork-on-chip channels and inter-chip routers.

In one embodiment, a neural network including at least one neurosynapticcore 310 may be implemented as a time-division multiplexed neurosynapticmodule. A neurosynaptic module is an electronic device comprising atleast one multi-way parallel processor.

Neurosynaptic networks may be configured or programmed in various ways.For example, neurosynaptic networks may be configured or programmed by aperson, or automatically by a computer system (e.g., via optimizationalgorithms, machine learning, etc.). As an option, neurosynapticnetworks may be programmed utilizing one or more reusable programblocks, which may also be referred to as “corelets.” After programmingis completed, neurons or synapses may remain connected or allocatedwithout having a destination to send spikes. For example, where a largeimage is received as input to a neurosynaptic network, and theneurosynaptic network only operates on a part of the image, neurons maybe allocated but not used.

Reducing the number of neurosynaptic cores 310 utilized to perform agiven task without affecting the functionality of a neurosynapticnetwork may save cost by reducing the total of chip sizes used.Moreover, reducing the number of neurosynaptic cores 310 utilized toperform a given task without affecting the functionality of theneurosynaptic network may save power during execution.

Accordingly, removing unused portions of a neurosynaptic network mayallow the neurosynaptic network to fit on a smaller, lower-cost chip, aswell as reduce power consumption during operation of the neurosynapticnetwork. In some circumstances, where a neurosynaptic network isduplicated and deployed in large quantities, the optimization may bedone once while the cost saving is multiplied by the number of deployedcopies of the neurosynaptic network.

Now referring to FIG. 4A, a flowchart of a method 400 for optimizingcore utilization in neurosynaptic systems is shown according to oneembodiment. The method 400 may be performed in accordance with thepresent invention in any of the environments depicted in FIGS. 1-3,among others, in various embodiments. Of course, more or less operationsthan those specifically described in FIG. 4A may be included in method400, as would be understood by one of skill in the art upon reading thepresent descriptions.

Each of the steps of the method 400 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 400 may be partially or entirely performed by aprocessor, or some other device having one or more processors therein.The processor, e.g., processing circuit(s), chip(s), and/or module(s)implemented in hardware and/or software, and preferably having at leastone hardware component, may be utilized in any device to perform one ormore steps of the method 400. Illustrative processors include, but arenot limited to, a central processing unit (CPU), an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), etc.,combinations thereof, or any other suitable computing device known inthe art.

As shown in FIG. 4A, method 400 initiates with operation 402, where oneor more unused portions of a neurosynaptic network are identified. Asdescribed above, the neurosynaptic network may comprise any network ofone or more neurosynaptic cores, wherein each of the neurosynaptic corescomprises axons and neurons, and corresponding axon paths, dendritepaths, and synapses.

An unused portion of the neurosynaptic network comprises any neuron oraxon that cannot affect the output of the neurosynaptic network. Forexample, if a given neuron has its output disconnected, then the neuroncannot affect the output of the neurosynaptic network.

More specifically, an unused axon may comprise an axon not connected toany source (e.g., a neuron, external source, etc.), or not connected toany destination (e.g., a crossbar, etc.). Moreover, an unused neuron maycomprise a neuron that is not connected to any source (e.g., a crossbar,etc.) and is not a spontaneous neuron, or is not connected to anydestination (e.g., an axon, an external destination, etc.). Aspontaneous neuron may comprise any neuron that spikes without input.Additionally, a silent neuron may comprise a neuron that, based on itsconfiguration, cannot ever spike independent of its synaptic input, ifany.

In one embodiment, unused portions of a neurosynaptic network may beidentified by scanning neurosynaptic cores of the neurosynaptic network.If a given neuron is determined to not be sending a spike outside of itsneurosynaptic core, and not sending a spike inside of its neurosynapticcore, then the neuron may not be being used, and may be identified as anunused portion of the neurosynaptic network.

Additionally, at operation 404, for each of the one or more unusedportions of the neurosynaptic network, the unused portion isdisconnected from the neurosynaptic network.

For a given neuron that has its output disconnected and cannot affectthe output of the neurosynaptic network, removing such a neuron anddisconnecting its inputs may free this neuron to perform other taskswithin the neurosynaptic network. As an option, removing such a neuronand disconnecting its inputs, and not connecting the neuron to performother tasks, may reduce a size of the neurosynaptic network.

In one embodiment, disconnecting the unused portions of theneurosynaptic network may include, for each unused neuron and unusedaxon, removing all intra-core connections (e.g., crossbar connections,etc.) of the unused neuron or unused axon, and removing all inter-coreconnections of the unused neuron or unused axon. Accordingly, when anunused portion of the neurosynaptic network is identified, all sources,crossbar connections, and destinations may be removed from the unusedportion. As an option, after removing all sources, crossbar connections,and destinations from the unused portion, a function of the unusedportion may be assigned to NULL.

In some embodiments, the operations 402 and 404 may be iterativelyrepeated until no unused portions are identified within theneurosynaptic network, and/or no additional axons and/or neurons may beremoved from the neurosynaptic network.

For example, referring to FIG. 4B, a flowchart of a method 450 foridentifying and removing one or more unused portions of a neurosynapticnetwork, is shown according to one embodiment. The method 450 may beperformed in accordance with the present invention in any of theenvironments depicted in FIGS. 1-3, among others, in variousembodiments. Of course, more or less operations than those specificallydescribed in FIG. 4B may be included in method 450, as would beunderstood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 450 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 450 may be partially or entirely performed by aprocessor, or some other device having one or more processors therein.The processor, e.g., processing circuit(s), chip(s), and/or module(s)implemented in hardware and/or software, and preferably having at leastone hardware component may be utilized in any device to perform one ormore steps of the method 450. Illustrative processors include, but arenot limited to, a central processing unit (CPU), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), etc.,combinations thereof, or any other suitable computing device known inthe art.

As shown in FIG. 4B, method 450 initiates with operation 452, where anyunused neurons within a neurosynaptic network are identified. If it isdetermined, at operation 454, that no unused neurons are identified,then the method may stop at operation 470. However, if unused neuronsare identified at operation 452, then, for each unused neuron, synapsesassociated with the unused neuron are removed at operation 456.

As a result of removing the synapses associated with the unused neurons,one or more axons within the neurosynaptic network may no longer beconnected. In other words, removing an unused neuron may in turn leaveone or more axons disconnected.

Accordingly, at operation 458, unused axons are identified, and each ofthe unused axons is removed at operation 460. Moreover, after removingthe unused axons at operation 460, neurons previously connected to suchaxons may now be identified as unused. Accordingly, unused neurons areagain identified at operation 452, and the method 450 may iterate untilno neurons and axons remain that are not affecting the output of theneurosynaptic network. In this manner, after disconnecting one or moreunused portions from the neurosynaptic network, one or more additionalunused portions of the neurosynaptic network may be identified anddisconnected. In other words, the method 450 may ensure that all unusedportions of a neurosynaptic network are removed.

An algorithm for identifying and disconnecting unused portions of theneurosynaptic network according to one specific embodiment is providedas pseudocode in Table 1. For a general graph, the algorithm of Table 1is guaranteed to terminate in at most n² steps, where n is the number ofneurons in the neurosynaptic network. Of course, such pseudocode isprovided as an option, and should not be construed as limiting in anymanner.

TABLE 1 Scan the network, add any unused neuron/axon to a queue. Whilethe queue is not empty: pop the first item from the queue. if it isunused add its neighbors (all its sources and destinations) to the queuedisconnect its sources, destinations, crossbar.□ mark it as NULL. end

Now referring to FIG. 5A, a flowchart of a method 500 for optimizingcore utilization in neurosynaptic systems is shown according to oneembodiment. The method 500 may be performed in accordance with thepresent invention in any of the environments depicted in FIGS. 1-3,among others, in various embodiments. Of course, more or less operationsthan those specifically described in FIG. 5A may be included in method500, as would be understood by one of skill in the art upon reading thepresent descriptions.

Each of the steps of the method 500 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 500 may be partially or entirely performed by aprocessor, or some other device having one or more processors therein.The processor, e.g., processing circuit(s), chip(s), and/or module(s)implemented in hardware and/or software, and preferably having at leastone hardware component may be utilized in any device to perform one ormore steps of the method 500. Illustrative processors include, but arenot limited to, a central processing unit (CPU), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), etc.,combinations thereof, or any other suitable computing device known inthe art.

As shown in FIG. 5A, method 500 may initiate with operation 502, whereindependent blocks of a first plurality of cores of a neurosynapticnetwork are identified.

As used herein, a block comprises at least a portion of a crossbar of aneurosynaptic core, and contains at least one neuron. In variousembodiments, each block comprises a portion of a crossbar of aneurosynaptic core, and contains one or more neurons connected to one ormore axons. Moreover, an independent block comprises a block for whichthere is no crossbar connection between any axon or neuron in the blockand a neuron or axon in another block. Accordingly, a first independentblock may be placed on the same core as a second independent block, oron a different core than the second independent block, without affectingthe output of either first independent block or the second independentblock.

For example, referring to FIG. 5B, a neurosynaptic core 510 isillustrated as containing a plurality of independent blocks. Theneurosynaptic core 510 may be substantially identical to theneurosynaptic core 310 previously described in the context of FIG. 3.

The neurosynaptic core 510 is illustrated to include axons 552 andneurons 554. While the neurosynaptic core 510 is illustrated to include32 axons 552 and 32 neurons 554, it is understood that the neurosynapticcore 510 may include any number of axons 552 and neurons 554. Still yet,the neurosynaptic core 510 is shown to include a plurality of connectedor conducting synapses 556. By way of example, synapse 556 a is shown toconnect axon number 4 with neuron number 16, synapse 556 b is shown toconnect axon number 16 with neuron number 18, and synapse 556 c is shownto connect axon number 10 with neuron number 27. As noted above, eachsynapse is located at a cross-point junction between an axon path and adendrite path, such that a connection between the axon path and thedendrite path is made through said synapse.

Moreover, the neurosynaptic core 510 is shown to include a plurality ofindependent blocks. In particular, Table 2 identifies five independentblocks included within the neurosynaptic core 510 of FIG. 5B.

TABLE 2 Block number Neurons Axons 1 3, 4 1 2 5, 6, 7, 8, 9, 12, 14, 15,16 2, 3, 4, 5, 6, 7, 14, 17 3 10, 11, 13, 18, 28, 29, 30 9, 11, 16, 19,20, 21 4 24, 25, 26, 27 10, 24, 25, 26 5 20, 21, 22, 23 22, 23, 30

Independent block number 2 of Table 2 is illustrated within FIG. 5B asindependent block 558. In particular, independent block 558 is shown toinclude axon numbers 2, 3, 4, 5, 6, 7, 14, and 17, and neuron numbers 5,6, 7, 8, 9, 12, 14, 15, and 16. For each of the axons and neurons in theindependent block 558, there are no crossbar connections to other axonsor neurons of another of the independent blocks. Accordingly, theindependent block 558 may be placed on the same core as any of the otherindependent blocks, or on a different core than the other independentblocks, without affecting the output of either independent block 558 orthe other independent blocks. Moreover, each of the independent blocksof FIG. 5B may be relocated to a neurosynaptic core other thanneurosynaptic core 510 without affecting the output of any of the otherindependent blocks.

While the independent blocks of Table 2 are shown to each include atleast one neuron and at least one axon, it is anticipated that in somecircumstance a single spontaneous neuron may comprise an independentblock.

The independent blocks of the neurosynaptic cores may be identified, atoperation 502, utilizing any suitable approach. In one embodiment, theneurosynaptic network may first be segmented into its constituentneurosynaptic cores. Further, each of the neurosynaptic cores may thenbe segmented into independent blocks.

As an option, segmenting a neurosynaptic core into independent blocksmay include selecting a first neuron of the neurosynaptic core, and thenidentifying all axons connected to the first neuron. The first neuronand the axons connected to the first neuron may be added to a list.Next, it may be determined whether additional neurons are connected toany of the axons identified as connected to the first neuron. Ifadditional neurons are identified, the additional neurons may be addedto the list. Further, this process may iteratively continue (i.e., byidentifying any additional axons that are connected to any of theadditional neurons, etc.) until no more axons and neurons are identifiedand added to the list. At the conclusion of the process, the list mayinclude all constituent axons and neurons that comprise an independentblock. Subsequently, a second neuron of the neurosynaptic core that isnot already identified as included in an independent block may beselected, and then axons and neurons connected to the second neuron maybe identified as comprising a second independent block. Additionalneurons may be selected and analyzed, until no additional neuronsremains that have not been identified as part of an independent block.

An algorithm for identifying independent blocks of cores of aneurosynaptic network according to one specific embodiment is providedas pseudocode in Table 3. The algorithm of Table 3 may be guaranteed toterminate in a linear time because, with each iteration, it marks oneneuron by its block ID. Of course, such pseudocode is provided as anoption, and should not be construed as limiting in any manner.

TABLE 3 For each core: mark all (used) neurons and all (used) axons as“unblocked” bi=1; % the block number while there are any “unblocked”neurons: empty queue Select first “unblocked” neuron and add it to thequeue while the queue is not empty pop first element mark it as “blockbi” add its neighbors on the crossbar to the queue end bi=bi+1 end

Additionally, the independent blocks are reconfigured onto the firstplurality of cores at operation 504. The independent blocks arereconfigured by calculating a new mapping for at least one of theindependent blocks, and moving the at least one of the independentblocks to a new location on a different core of the neurosynapticnetwork in accordance with the new mapping.

An independent block may be moved to a new location on a differentneurosynaptic core by configuring the axons, neurons, and crossbar ofthe different neurosynaptic core with the functionality provided by theindependent block on its original neurosynaptic core, and routing allinput/output connections of the independent block to the independentblock on the different neurosynaptic core.

New mappings for the independent blocks may be calculated utilizing anysuitable approach. In one embodiment, the new mappings may be calculatedby sorting the independent blocks of the neurosynaptic cores into twolists. A first list of the two lists may include the independent blocksof the neurosynaptic cores in decreasing order of the number of axons ineach independent block. A second list of the two lists may include theindependent blocks of the neurosynaptic cores in decreasing order of thenumber of neurons in each independent block. Further, a first one of theneurosynaptic cores may be selected and filled by iteratively picking anindependent block from the top of one of the two lists, and mapping theindependent block to the core.

An independent block may be picked by comparing a largest dimension of afirst independent block at the top of the first list (i.e., a number ofaxons in the first independent block, or number of neurons in the firstindependent block, whichever is larger), with a largest dimension of asecond independent block at the top of the second list (i.e., a numberof axons in the second independent block, or number of neurons in thesecond independent block, whichever is larger). Next, the independentblock having the largest larger value may then be picked for placementon the selected neurosynaptic core.

Additionally, if there are more remaining axons than neurons, a firstfitting independent block may be picked from the first list includingthe independent blocks of the neurosynaptic cores in decreasing order ofthe number of axons in each independent block. However, if there are notmore remaining axons than neurons, a first fitting independent block maybe picked from the second list including the independent blocks of theneurosynaptic cores in decreasing order of the number of neurons in eachindependent block.

Additional independent blocks may be picked and placed on the firstselected neurosynaptic core until the first selected neurosynaptic corehas been filled (i.e., no additional independent blocks can fit on aremaining area of the crossbar of the neurosynaptic core), at whichpoint a second neurosynaptic core may be selected and filled in the samemanner. This process may continue until all independent blocks have beenplaced. Moreover, this process may effectively balance neuron-dominantand axon-dominant blocks and fit them together on the same neurosynapticcores, thereby maximizing the usage of both the axons and neurons oneach neurosynaptic core, as shown below in the context of FIGS. 6A, 6B,and 6C.

An algorithm for reconfiguring the independent blocks onto a pluralityof cores according to one specific embodiment is provided as pseudocodein Table 4. Of course, such pseudocode is provided as an option, andshould not be construed as limiting in any manner.

TABLE 4 Input: a set of n blocks, b_1..b_n Output: an assigned corenumber c_i (in C) for each b_i Objective: minimize the total number ofcores (the size of C) Let n_i and a_i denote the number of neurons andthe number of axons in block b_i, respectively. 1. Sort all blocks ontwo lists, one is in decreasing order of a_i and the other is bydecreasing order of n_i. 2. Use dynamic programming for filling up thenext core: pick up the top block from one of the two lists, for whichthe larger dimension is the largest. Place it on the core. Repeat Ifthere are more remaining axons than neurons, take first-fit from the a_ilist. Else, take first-fit from the n_i list. Until no block can fit onthe remaining area of the crossbar

Reconfiguring the independent blocks onto the neurosynaptic cores of theneurosynaptic network may be limited by constraints uncharacteristic oftypical tiling problems. In particular, when an independent block isplaced on a neurosynaptic core, although the independent block mayoccupy only a small subset of the synapses of the neurosynaptic core, noother independent block may be placed on any axon path or dendrite pathutilized by the independent block. Or, in other words, no otherindependent block may occupy a synapse that is in communication with anaxon in the horizontal direction, or a neuron in the vertical direction,included in the independent block.

In one embodiment, wherein each core comprises an array of 256neurons×256 axons, each independent block comprises a tile of tiles T₁,. . . , T_(m) of integral sizes w_(i)×h_(i), where 1≤w_(i), h_(i)≤256,and i=1, . . . , m. Each of the tiles is assigned to one of n sites(i.e., cores) S₁, . . . , S_(n), and the number of utilized sites may beminimized as follows. Denote by y_(j) a Boolean variable so that y_(j)=1if and only if site is utilized; and denote by x_(ij) a Boolean variableso that x_(ij)=1 if and only if tile T_(i) is assigned to site S_(j).Accordingly,

$\sum\limits_{j = 1}^{n}\; y_{j}$

may be minimized subject to:

${\sum\limits_{j = 1}^{n}\; x_{ij}} = {1\mspace{14mu} \left( {{i = 1},\ldots \;,m} \right)}$${\sum\limits_{i = 1}^{m}\; {w_{i}x_{ij}}} \leq {256y_{j}\mspace{14mu} \left( {{j = 1},\ldots \;,n} \right)}$${\sum\limits_{i = 1}^{m}\; {h_{i}x_{ij}}} \leq {256y_{j}\mspace{14mu} \left( {{j = 1},\ldots \;,n} \right)}$x_(ij), y_(j) ∈ {0, 1}.

In another embodiment, wherein each core comprises an array of 256neurons×256 axons, each independent block comprises a tile that is oneof k types of tiles, where there are k_(i) tiles of type i (i=1, . . . ,k), each of a size w_(i)×h_(i), and where 1≤w_(i), h_(i)≤256. Each ofthe tiles is assigned to one of n sites (i.e., cores) S₁, . . . , S_(n),and the number of utilized sites may be minimized as follows. Denote byy_(j) a Boolean variable so that y_(i)=1 if and only if site S_(j) isutilized; and denote by x_(ij) an integral variable so that x_(ij) isthe number of tiles of type i that are assigned to a site S_(j).Accordingly,

$\sum\limits_{j = 1}^{n}\; y_{j}$

may be minimized subject to:

${\sum\limits_{j = 1}^{n}\; x_{ij}} = {w_{i}\mspace{14mu} \left( {{i = 1},\ldots \;,k} \right)}$${\sum\limits_{i = 1}^{k}\; {w_{i}x_{ij}}} \leq {256y_{j}\mspace{14mu} \left( {{j = 1},\ldots \;,n} \right)}$${\sum\limits_{i = 1}^{k}\; {h_{i}x_{ij}}} \leq {256y_{j}\mspace{14mu} \left( {{j = 1},\ldots \;,n} \right)}$x_(ij)  is  integer, y_(j) ∈ {0, 1}.

A model for solving the optimal packing problem with a minimal number ofsites, where each tile is one of k types of tiles, is provided as IBMOptimization Programming Language (OPL) code in Table 5. Of course, suchcode is provided as an option, and should not be construed as limitingin any manner.

TABLE 5 int numTypes = ... ; range Types = 1..numTypes ; intnumTiles[Types] = ... ; int numSites = ... ; range Sites = 1..numSites ;float width[Types] = ... ; float height[Types] = ... ; dvar int+x[Types] [Sites]; dvar boolean y[Sites]; minimize sum (j in Sites) y[j]; subject to { forall (i in Types) sum (j in Sites) x[i][j] ==numTiles[i] ; forall (j in Sites) sum (i in Types) width[i]*x[i][j] <=256 * y[j]; forall (j in Sites) sum (i in Types) height[i]*x[i][j] <=256 * y[j]; }

Referring now to FIGS. 6A and 6B, two neurosynaptic cores of anon-optimized neurosynaptic network 600 are shown. In particular, Core Ais shown to include a plurality of splitters 612, where each splittermay operate to receive a spike from a given axon, and split the spike toseveral receiving neurons. For simplicity, each of the splitters 612 ofFIG. 6A is shown to split a spike received from an axon to fourreceiving neurons. Further, none of the splitters 612 is connected toanother one of the splitters 612, and each coupling of one axon to fourneurons may be identified as an independent block.

Similarly, Core B is shown in FIG. 6B to include a plurality of summers614. Each of the summers 614 may operate to sum the spikes of severalaxons, and provide the result to a single neuron. As an option, each ofthe summers 614 may comprise a weighted summer. For simplicity, each ofthe summers 614 of FIG. 6B is shown to sum the spikes received from fouraxons, and provide the result to a single neuron. Further, none of thesummers 614 are connected to another one of the summers 614, and eachcoupling of four axons to one neuron may be identified as an independentblock.

Core A is shown to include a significant number of unused axons 602, andCore B is shown to include a significant number of unused neurons 604.More specifically, as illustrated by FIG. 6B, because there are noadditional free neurons in Core A, the unused axons 602 of Core A willremain disconnected and unused because no additional independent blocksmay be added without interfering with the operation of the currentlyconfigured splitters 612. Similarly, because there are no additionalfree axons in Core B, the unused neurons 604 of Core B will remainunused and disconnected. In other words, as a result of theconfigurations of Core A and Core B, a significant number of neurons andaxons may go completely unutilized. Accordingly, neither Core A nor CoreB may currently be configured in an optimal manner.

Referring now to FIG. 6C, Core A is shown after executing the method ofFIG. 5A, wherein the independent blocks of Cores A and B are identified,and then reconfigured using new mappings that increase the overallefficiency of the neurosynaptic network 600. As illustrated by FIG. 6C,some of the summers 614 and some of the splitters 612 may be combinedonto the same core such that almost all neurons and all axons of Core Aare utilized. As a consequence, fewer neurosynaptic cores may berequired to allocate the same number of independent blocks and achievethe same functionality.

In some embodiments, the calculation of the new mappings and cores forthe independent blocks may be simplified. For example, the aboveoptimization problem, wherein independent blocks are picked and placed,may be mapped to a simplified problem by grouping together two or moretypes of independent blocks of similar sizes. Next, each independentblock of the group may be replaced with one independent block type ofdimensions greater or equal to the maximum of the dimensions of the eachblock type in the group.

For example, if provided 4 independent blocks of size 20×30 (e.g., 20axons×30 neurons, or 20 neurons×30 axons), 2 independent blocks of size22×28, and one independent block of size 20×31, then these three typesof independent blocks may be grouped together. Specifically, each ofthese 7 independent blocks may be replaced with one type of independentblock, the one type of independent block having a size of 22×31. Once alocation is found on neurosynaptic cores for each of the seven 22×31independent blocks, then each of the original independent blocks may bemapped to and placed in one of these locations. Because each of theoriginal independent blocks may be smaller than the 22×31 block type, afew axons and a few neurons may be left unused.

In other embodiments, the optimization problem, wherein independentblocks are picked and placed, may be split into several problems byfirst placing only the largest independent block types on cores, thenadding more smaller independent blocks and restarting the optimization,and continuing to solve while each iteration places large independentblocks and adds more small independent blocks.

In some embodiments, a neurosynaptic network may be divided into severalparts or partitions, each of which may be optimized separately andindependently. As an option, two or more of the partitions may beoptimized in parallel. Partitioning the independent blocks intoindependent parts may ensure that each part is kept on independentcores, and may accelerate the optimization process.

In some embodiments, a neurosynaptic network may be divided byfeed-forward traversal of the graph, and split into regions byproximity. Each of these regions can be independently optimized andrecombined.

Additionally, after the independent blocks have been reconfigured,block-to-block connectivity may be updated for each of the independentblocks. In other words, because the outputs of one block may be providedas input to one or more other blocks (whether on the same neurosynapticcore or on a different neurosynaptic core), after the independent blockshave been reconfigured, connectivity between the independent blocks maybe updated to maintain any such input/output relationships between theblocks.

In some embodiments, a neurosynaptic network may comprise neurosynapticcores having different properties. For example, a given neurosynapticnetwork may comprise first neurosynaptic cores all having a same firstproperty, and second neurosynaptic cores all having a same secondproperty. The second property may be different from the first property.For example, all of the first neurosynaptic cores may be of a first size(e.g., axon×neuron dimension), and all of the second neurosynaptic coresmay be of a second size, which is different than the first size.

In such an example, the second sized neurosynaptic cores may be largeror smaller than the first sized neurosynaptic cores. It may beinefficient to place many small independent blocks on a largeneurosynaptic core. Accordingly, it may be more efficient to place thesmaller independent blocks on the smaller neurosynaptic cores, and thelarger independent blocks on the larger neurosynaptic cores. In such ascenario, a cost function may associate a cost with unused parts of acrossbar (i.e., parts of the crossbar that are not covered by any blocksthat are assigned to the core). By searching to minimize one or morecost functions, a cost function may be utilized to optimize overallneurosynaptic core utilization.

In some embodiments, one or more independent blocks may be marked asunmoveable. As an option, an unmoveable block may be a block that isassociated with input that originates from outside of the neurosynapticnetwork, or provides output that is destined for a location outside ofthe neurosynaptic network. Accordingly, in such embodiments, identifyingthe independent blocks of a plurality of cores may include identifyingonly moveable independent blocks of the cores, such that unmoveableindependent blocks of the cores are not reconfigured. This may ensurethat any optimization only applies to those blocks that may be moved todifferent cores without adverse effects on the function of theneurosynaptic network.

In some embodiments, not all neurosynaptic cores of a neurosynapticnetwork may have the same properties or be operating in an identicalmanner. For example, some of the neurosynaptic cores may operate at afirst time scale, and other neurosynaptic cores may operate at a secondtime scale that is faster or slower than the first time scale. As aconsequence, the neurosynaptic cores across a given neurosynapticnetwork may be operating a two ore more different time scales. In suchcircumstances, a block may not be moved from a neurosynaptic coreoperating at a first time scale to a different neurosynaptic core thatis operating at a different time scale.

Accordingly, in such embodiments, the operations of the method 500 mayoccur independently for each time scale to ensure that blocks are onlymoved to other neurosynaptic cores operating at the same time scale asthe neurosynaptic core that the block originates from. In other words,the cores of a neurosynaptic network may be independently sub-optimizedwithin classes of cores, where each class of cores comprises cores thathave the same properties, or are operating in an identical manner.

In some embodiments, the location of an independent block may beselected such that it maximizes connectivity of the independent blockwith other independent blocks on the same core. This may reduce theconnectivity present between two or more cores, and may providebandwidth, latency, and energy benefits. In other words, while any blockof m×n dimensions may fit at a given location of equal or largerdimensions, there may be an advantage to selecting a specificindependent block for the location based on other criteria (e.g.,connectivity, etc.). Similarly, the new location of a reconfiguredindependent block may be selected to maximize an expected spike ratebetween the block and other blocks on the same core, thereby minimizingthe external spike rate coming from the neurosynaptic core and destinedfor other cores. The process of maximizing connectivity and/or anexpected spike rate may occur in parallel with, or after, thereconfiguring of the independent blocks based on size.

In one embodiment, the method 500 is performed on a neurosynapticnetwork after performance of the method 400 on the neuro synapticnetwork. In other words, after identifying and removing one or moreunused portions of a neurosynaptic network, independent blocks of theneurosynaptic network may be identified and reconfigured onto theneurosynaptic cores of the neurosynaptic network. By combining themethods 400 and 500, neurosynaptic core utilization may be optimizedthroughout the neurosynaptic network.

In the embodiments described hereinabove, one or more neurosynapticcores of a neurosynaptic network may be analyzed, and then modified toreduce the number of utilized cores while preserving the computationalfunctionality of the original neuro synaptic network. In other words,the resulting neurosynaptic network may perform the same computation asthe original neurosynaptic network while reducing a footprint of thenetwork and/or consuming less power. As set forth above, such a benefitmay be realized by identifying and removing unused portions of theneurosynaptic network, splitting one or more cores into independentblocks, and moving at least a portion of the independent blocks to othercores without affecting the overall network functionality.

The methods and systems described hereinabove may apply to any network,regardless of how the network was generated. Further, because theabove-described optimization occurs after the network has been created,code optimization may not need to be a focus, or even a concern, whilegenerating code that creates such networks having complex functionality.As a result, a programmer may be able to focus on the functionality ofsuch network code, and allow the optimization to be performedsubsequently in an automated manner. Additionally, because the methodsand systems described hereinabove consider all network components atonce, such optimizations may be able to exploit advantages not presentduring code generation or authorship. In other words, due to limitedknowledge and/or access, an author of a first portion of network codemay not be able to co-locate onto a given core blocks from the firstportion of network code with blocks from another portion of the networkcode.

Still yet, the network code may be optimized by different algorithms,without requiring a rebuild of the neurosynaptic systems. Even more, theoptimization may even be applied on the output of previously optimizedcomponents and networks, such as, for example, in the case of using alinker.

As an option, in a fixed-size neurosynaptic chip or neurosynaptic systemwith a given number of neurosynaptic cores, one may apply optimizationand then use the cores freed by the optimization to add additionalfunctionality, or to improve computation accuracy, and therefore improvea final product without incurring additional hardware costs.Additionally, reducing the number of neurosynaptic cores may savememory, processing cycles, and/or number of processors; and increasespeed, reduce power, and/or reduce overall processing time.

As another option, in energy-sensitive systems, such as mobile systems,airborne systems, satellites, remote sensors, etc., reducing the numberof cores may reduce energy consumption of the system.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a FPGA, etc. By executable by theprocessor, what is meant is that the logic is hardware logic; softwarelogic such as firmware, part of an operating system, part of anapplication program; etc., or some combination of hardware and softwarelogic that is accessible by the processor and configured to cause theprocessor to perform some functionality upon execution by the processor.Software logic may be stored on local and/or remote memory of any memorytype, as known in the art. Any processor known in the art may be used,such as a software processor module and/or a hardware processor such asan ASIC, a FPGA, a central processing unit (CPU), an integrated circuit(IC), a graphics processing unit (GPU), etc.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer to offer service on demand.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A computer program product for optimizing coreutilization in a neurosynaptic network, the computer program productcomprising a computer readable storage medium having programinstructions embodied therewith, wherein the computer readable storagemedium is not a transitory signal per se, the program instructionsexecutable by a processor to cause the processor to perform a methodcomprising: identifying, by the processor, one or more unused portionsof a neurosynaptic network; and for each of the one or more unusedportions of the neurosynaptic network, disconnecting, by the processor,the unused portion from the neurosynaptic network.
 2. The computerprogram product of claim 1, wherein each of the one or more unusedportions comprises one of an unused neuron and an unused axon.
 3. Thecomputer program product of claim 2, wherein an unused neuron comprisesa neuron that cannot affect an output of the neurosynaptic network, andan unused axon comprises an axon that cannot affect the output of theneurosynaptic network.
 4. The computer program product of claim 2,wherein identifying the one or more unused portions of the neurosynapticnetwork includes: scanning the neurosynaptic network to identify theunused neurons and the unused axons; and adding the identified unusedneurons and the identified unused axons to a queue.
 5. The computerprogram product of claim 4, wherein, for each unused portion in thequeue, disconnecting the unused portion from the neurosynaptic networkincludes disconnecting the unused portion from at least one of a source,a destination, a connection, and a crossbar.
 6. The computer programproduct of claim 2, further comprising, after disconnecting each of theone or more unused portions from the neurosynaptic network: identifying,by the processor, one or more additional unused portions of theneurosynaptic network; and for each of the one or more additional unusedportions of the neurosynaptic network, disconnecting, by the processor,the additional unused portion from the neurosynaptic network.
 7. Asystem, comprising: a processor; and logic integrated with theprocessor, executable by the processor, or integrated with andexecutable by the processor, the logic being configured to: identify oneor more unused portions of a neurosynaptic network; and for each of theone or more unused portions of the neurosynaptic network, disconnect theunused portion from the neurosynaptic network.
 8. The system of claim 7,wherein each of the one or more unused portions comprises one of anunused neuron and an unused axon.
 9. The system of claim 8, wherein anunused neuron comprises a neuron that cannot affect an output of theneurosynaptic network, and an unused axon comprises an axon that cannotaffect the output of the neurosynaptic network.
 10. The system of claim8, wherein identifying the one or more unused portions of theneurosynaptic network includes: scanning the neurosynaptic network toidentify the unused neurons and the unused axons; and adding theidentified unused neurons and the identified unused axons to a queue.11. The system of claim 10, wherein, for each unused portion in thequeue, disconnecting the unused portion from the neurosynaptic networkincludes disconnecting the unused portion from at least one of a source,a destination, a connection, and a crossbar.
 12. The system of claim 8,where the logic is further configured to, after disconnecting each ofthe one or more unused portions from the neurosynaptic network: identifyone or more additional unused portions of the neurosynaptic network; andfor each of the one or more additional unused portions of theneurosynaptic network, disconnect the additional unused portion from theneurosynaptic network.
 13. A computer program product for optimizingcore utilization in a neurosynaptic network, the computer programproduct comprising a computer readable storage medium having programinstructions embodied therewith, wherein the computer readable storagemedium is not a transitory signal per se, the program instructionsexecutable by a processor to cause the processor to perform a methodcomprising: identifying, by the processor, independent blocks of a firstplurality of cores of a neurosynaptic network; and reconfiguring, by theprocessor, the independent blocks onto the first plurality of cores bycalculating a new mapping for at least one of the independent blocks,and moving, by the processor, the at least one of the independent blocksto a new location on a different core of the first plurality of cores ofthe neurosynaptic network in accordance with the new mapping.
 14. Thecomputer program product of claim 13, further comprising updatingblock-to-block connectivity for each of the at least one of theindependent blocks moved to a new location.
 15. The computer programproduct of claim 13, wherein the neurosynaptic network further comprisesa second plurality of cores, wherein all cores of the first plurality ofcores have a same first property, and all cores of the second pluralityof cores have a same second property, wherein the first property isdifferent than the second property.
 16. The computer program product ofclaim 15, wherein the first property includes a first time scale, andthe second property includes a second time scale.
 17. The computerprogram product of claim 13, wherein identifying the independent blocksof the first plurality of cores includes identifying only moveableindependent blocks of the first plurality of cores, such that unmoveableindependent blocks of the first plurality of cores are not reconfigured.18. The computer program product of claim 13, wherein the firstplurality of cores includes cores of different sizes.
 19. The computerprogram product of claim 18, wherein a cost function is utilized forreconfiguring the independent blocks onto the first plurality of cores.20. The computer program product of claim 19, wherein the cost functionis minimized.